title: Chiral, hemilabile palladium(II) complexes of tridentate oxazolidines, including C2-symmetric "pincers".
abstract: Two classes of diastereomerically enriched chiral tridentate ligands incorporating either two oxazolidine and one pyridine ( 1) or two pyridine and one oxazolidine ( 2a-c) donor groups have been made in a high-yielding modular fashion from readily available enantiopure amino alcohols and aldehydes. Both ligand classes readily formed metal complexes via 1:1 reactions with trans-PdCl 2(PhCN) 2. The compounds Pd( 1)Cl 2 and Pd( 2a-c)Cl 2 were formed as mixtures of 3 and 2 diastereomers, respectively, owing to indeterminate absolute configuration at the C (2) position of their constituent oxazolidine rings. Within each diastereomeric manifold, the metal complexes existed as equilibrium mixtures of bi- and tridentate isomers in solution, the interconversion between which was very rapid even at -50 degrees C. The fluxional nature of the compounds was inferred from a combination of (1)H and (15)N NMR spectroscopic and solution conductivity data. Substitution of one chloride ligand for hexafluorophosphate gave as mixtures of diastereomers the salts [Pd( 1-kappa N,kappa (2) N')Cl]PF 6 ( 8) and [Pd( 2a-c-kappa N,kappa N',kappa N'')Cl]PF 6 ( 12a-c) in which the ligands were coordinated through all three N-donors. A single recrystallization of 8 gave in optically pure form the major diastereomer 8 ( maj ), which was characterized crystallographically. Complexes of 2a-c differed substantially from those of the bis(pyridylmethyl)amine (bpma) ligand family with which they shared direct atom-for-atom connectivity in the coordinating groups. The amines are known to form exclusively the static tridentate complexes [PdCl(bpma-kappa N,kappa (2) N')]Cl; the difference was attributed to torsional strain associated with the rigid oxazolidine ring in tricoordinated 2a-c.
authors.affiliation: Department of Chemistry, The University of Western Ontario, London, Ontario, Canada N6A 5B7.
authors.forename: Elizabeth T J
authors.initials: ET
authors.lastname: Strong
authors.forename: Steven A
authors.initials: SA
authors.lastname: Cardile
authors.forename: Allison L
authors.initials: AL
authors.lastname: Brazeau
authors.forename: Michael C
authors.initials: MC
authors.lastname: Jennings
authors.forename: Robert
authors.initials: R
authors.lastname: McDonald
authors.forename: Nathan D
authors.initials: ND
authors.lastname: Jones